The present invention relates to an auxiliary power unit (APU), methods of operating an APU and a vehicle comprising said APU and/or said method.
One way to provide electric power and heat to the truck driver's welfare when not driving the truck is to use the engine as a power source. This is often an inefficient way to produce electricity and heat both from fuel consumption and emission aspects, and will also be subject to legal restrictions in the near future. Typical engine effiencieny at idle is around 5-10%. One way which this is solved is with an auxiliary power unit (APU) consisting of a fuel processor for converting diesel to hydrogen and a fuel cell for converting hydrogen to water and electric power.
To lower the demand for oil, there are ongoing work for alternative fuels. One alternative fuel is dimethyl ether (DME). For these vehicles there will also be a need for an APU. A fuel processor for DME may be simpler in construction than a diesel fuel processor with lower working temperature and fewer gas cleaning steps. In EP01060535B1 a fuel cell able to be used with DME as feed is described. With this fuel cell the APU can be simplified to just a fuel cell, water recovery, cooling and fuel and air pumping to the fuel cell.
However, a problem with DME is its very low lubricating properties. Therefore there is a need to mix DME with a small amount of lubricant before sold as fuel. This lubricant may have very different properties for fuel processing and may eventually cause the DME fuel processor to make gases not suited for a fuel cell. Another problem with APU's is the need of water to the fuel processor and the fuel cell, this is solved by condensing water from the fuel cells off-gases see e.g., U.S. Pat. No. 7,036,466B2. The cooling for the water condensing could be arranged by blowing ambient air by a fan. However this cost energy for the fan and can also be inefficient and even impossible in some climate due to the low condensing temperature needed. Some solutions of the latter is described in U.S. Pat. No. 6,759,154 and DE10337607.
As explained above, there is a problem associated with DME mixed with lubricant for the functionality and/or properties for the fuel cell in an APU.
It is desirable to provide an APU in which the above mentioned problem with DME mixed with lubricants is at least reduced or eliminated.
In a first example embodiment an auxiliary power unit (APU) comprising a fuel processor and a fuel cell, said fuel processor is provided with steam, air and DME. Said APU further comprising an afterburner for combusting rest fuel from the fuel cell, wherein exhaust gases from said afterburner is used for heating a first heat exchanger. Said fuel processor is preparing the vehicle fuel to a fuel suitable for the fuel cell and said fuel processor is provided between said fuel reservoir and said fuel cell. The interpretation of preparing is meant to include for instance one or more of the following: transformations, distillations, any form of reactions, adsorptions, absorptions, change of state of aggregation, mixtures, solutions, etc.
In another example embodiment said first heat exchanger has at least one inlet and at least one outlet, said at least one inlet is provided with DME comprising a lubricant from a fuel tank. Said at least one outlet from said first heat exchanger is providing clean DME, and said lubricant is trapped in said first heat exchanger.
In still another example embodiment the APU further comprising a second heat exchanger, said second heat exchanger is connected to the exhaust gases from said after burner, said second heat exchanger further comprising at least one inlet and at least one outlet, said at least one inlet is connected to a condenser with condensed water from the fuel cell, said outlet is connected to said fuel processor for providing steam to said fuel processor.
In still another example embodiment said first heat exchanger and said second heat exchanger is the same unit.
In still another example embodiment said first heat exchanger is heated by gases from a water condenser.
In still another example embodiment said first heat exchanger has a DME fuel inlet and DME gas outlet and a lubricant outlet.
In still another example embodiment said first heat exchanger has a gas inlet and gas outlet and an outlet for condensed water.
In still another example embodiment said first heat exchanger is heated by cooling water from the fuel cell.
In still another example embodiment said first heat exchanger has a DME fuel inlet and DME gas outlet and a lubricant outlet.
In still another example embodiment said first heat exchanger has a cooling water inlet and cooling water outlet.
It is desirable to provide an auxiliary power unit process in which the above mentioned problem with DME mixed with lubricant is at least reduced or eliminated.
In a first example embodiment an auxiliary power unit process comprising the actions of providing air, steam and DME fuel to fuel processor unit, extracting at least hydrogen from said fuel processor unit, providing said hydrogen and air to a fuel cell, condensing water extracted from said fuel cell in a condenser, combusting rest fuel from the fuel cell in an after burner, separating a lubricant from a DME fuel before providing said DME fuel to the fuel processor unit.
In another example embodiment of the auxiliary power unit process, said separating of DME and lubricant is performed by using exhaust gases from said after burner in a first heat exchanger.
In still another example embodiment said first heat exchanger is heated by gases from a water condenser.
In still another example embodiment said first heat exchanger has a DME fuel inlet and DME gas outlet and a lubricant outlet.
In still another example embodiment said first heat exchanger has a gas inlet and gas outlet and an outlet for condensed water.
In still another example embodiment said first heat exchanger is heated by cooling water from the fuel cell.
In still another example embodiment said first heat exchanger has a DME fuel inlet and DME gas outlet and a lubricant outlet.
In still another example embodiment said first heat exchanger has a cooling water inlet and cooling water outlet.
In yet another example embodiment the auxiliary power unit process further comprising the action of providing steam to said fuel processor by heating said water from said condenser in a second heat exchanger heated by said exhaust gases from said after burner.
In still another example embodiment of the auxiliary power unit process said first heat exchanger for providing steam is the same heat exchanger as the second heat exchanger for separating the lubricant from the DME fuel.
The present invention also relates to a vehicle provided with an engine for traction power, an auxiliary power unit (APU) and a reservoir of fuel. Said fuel is used for running said engine and said APU. Said APU comprising a fuel processor and a fuel cell, wherein said fuel processor is provided between said fuel reservoir and said fuel cell. Said fuel is dimethyl ether (DME), wherein means is provided for separating said DME fuel from at least one lubricant included in said DME.